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The small size of bacteria is also beneficial for parasitism and oligotrophy. Because various microorganisms are absent in such environments, bacteria successfully exploit resources available and thrive in such environments. These include such environments as the vertical gradients in intertidal marine sediments in which various types of bacteria have been found. Research studies have shown their size to play an important role in survival over time.ĭue to their small size, bacteria are able to exploit and thrive in various microenvironments. , accessed January 14, 2005.In general, bacteria are between 0.2 and 2.0 um - the average size of most bacteria. (9) Teachers Experiencing Antarctica and the Arctic. (8) Biology at the University of Cincinnati Clermont College. (6) "Bacterial Colony Morphology." Austin Community College. (5) "Bacterial Colony Morphology." Austin Community College. (4) "Bacterial Colony Morphology." Austin Community College. (3) "Bacterial Colony Morphology." Austin Community College. (2) "Microbiology 101 Laboratory Manual." Washington State University. (1) "Microbiology 101 Laboratory Manual." Washington State University. Most bacterial colonies appear white, cream, or yellow in color, and fairly circular in shape.įinally, whenever a thorough, visual identification is not possible, examples of additional tests are gram stains ( ), growths on selective media, and enzymatic tests. Being kept in one place, the resulting cells have accumulated to form a visible patch. What Can Grow on a Nutrient Agar Plate? BacteriaĮach distinct circular colony should represent an individual bacterial cell or group that has divided repeatedly. A lobate margin has rounded finger-like growths that spread outward. A curled margin appears as wave-like layers spreading outward. A filiform margin has small branch like growth that spreads outward. Bacteria can grow with a bumpy edge called undulate. The margin growth of a bacteria describes how the edges of the colony appear under a microscope and can appear: with a smooth rounded edge called entire. The elevation of bacteria describes how they grow upwards: raised in a shallow dome shape, convex growth in a steep dome shape, flat growth parallel to the ground, umbonate growth with a small raised bump in the center, and crateriform growth has a raised profile with a concave dip in the center. The bacterias form describes how they spread in a petri dish and can be: circular (covering the whole dish) irregular (spreading out in a non-uniform pattern), filamentous (spreading out like roots towards the outer edge), and rhizoid (spreading out like branches with main segments splitting into smaller segments). Refer to the diagram below for illustrated examples of form, elevation, and margin: (2)Ĭommon physical characteristics of bacteria colonies are listed and separated into 3 categories. Please note that 3 additional elements of morphology should be examined only in a supervised laboratory setting: consistency, emulsifiability, and odor. Chromogenesis (pigmentation) - For example, white, buff, red, purple, etc.Opacity - For example, transparent (clear), opaque, translucent (almost clear, but distorted vision, like looking through frosted glass), iridescent (changing colors in reflected light), etc.Surface - How does the surface of the colony appear? For example, smooth, glistening, rough, dull (opposite of glistening), rugose (wrinkled), etc.Margin - What is the magnified shape of the edge of the colony?.Elevation - What is the cross sectional shape of the colony? Turn the Petri dish on end.
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